The present invention relates in general to a source of ultraviolet radiation and in particular to a method of and device for changing or adjusting the intensity and effects of ultraviolet radiation.
Ultraviolet radiation, in the following text referred to a UV-radiation, is divided according to its wavelengths into UVA-, UVB- and UVC radiation bands. The UVA band has a wavelength between 315 and 400 nl and its share in the sunlight amounts to about 5%. The UVB radiation band has a wavelength from 280 to 315 nm and in the European geographical latitudes constitutes about 0.04 to 0.12% of sunlight. The UVC radiation band has its wavelengths in the range between 200 and 280 nm which even if emitted by sun, are blocked by the earth's atmosphere.
The effect of UV radiation is manysided. For example, human skin becomes tanned in response to the exposure of UVB- and UVA radiation. The UVC radiation generates ozone in the atmosphere and in addition, destroys microorganisms such as bacteria, viruses, spores, yeast, algaes, protozoa and mold fungi. In the human skin, UVC radiation produces histamin, causing sunburn, and destroys bacteria which interfere with regulation of fatty films. The radiation therapy employs UV radiation for healing purposes, and in photochemistry the UV radiation enhances chemical reactions.
In utilizing UV radiation, different types of radiation sources and irradiation devices have been developed in order to transmit the desired radiation band such as UVA- and/or UVB, or UVC radiation band. The intensity of radiation and the wavelength range generated in such prior-art devices is normally constant. Of course, the intensity can be adjusted by conventional filters or by electrical means, for example, by switching on or off individual radiation sources when the device includes a plurality of light sources transmitting at different wavelengths. This dosing capability for controlling the time of irradiation however is in most cases insufficient especially when it is desired to adjust the exposure or dose to skin conditions of individual patients. For example, the sensitivity of different parts of the human body to radiation is not uniform. While abdomen, breast or back can withstand 75 to 100% of a certain dose of irradiation, the sensitivity of the lower arm or of the surface of the shinbone can tolerate only 25% of this dose. Moreover, the permissible dose depends on age, on hair color, on sex and other constitutional and racial peculiarities as well as on year's season and condition of toners of the vegetative nervous system. At present time, the dosimetry is based on the generation of erythrism, that means it is concerned with the sensitivity of human skin defining a maximum sensitivity at 296.7 nm (finsen). The measure for effectiveness of the radiation relates to a fictitious "average person" so that the individual dose must be ascertained empirically. The same considerations are valid in dosing radiation for photochemical and the like processes in which UV radiation is used.
In known phototherapy apparatuses or solaria, the intensity of radiation (radiation strength in finses) is adjustable by varying the number of active radiations and their mutual arrangement, by adjusting the distance from the plane of radiation, and by varying exposure time. In addition, it is known to employ filters for absorbing certain wavelengths, the effect of which may be harmful. Furthermore, large area solaria have been developed which permit the irradiation of the whole body of a patient, whereby the distribution of intensity of radiation is adjusted to different sensitivities of various parts of the patient's body. This known intensity adjustment is attainable by the application of different filters and/or radiation sources transmitting at different intensities or wavelengths. Such diversified radiation sources are arranged in the radiation plane of the apparatus according to the outlines of the body to be irradiated. This solution however, is suitable for relatively small transmitting distances only, for example when the spacing between the source and the object to be irradiated is smaller than one meter but even in this case the results are not completely satisfactory.
Known also are the so-called "home suns" which denotes radiation sources using mercury vapor lamps as well as electrically heated rods for transmitting infrared (IR) radiation. The ultraviolet rays of mercury vapor lamps are used in irradiating skin in order to achieve therapeutic and cosmetic effects and/or to increase the resistance of the human body. The ultraviolet rays, as known, assist in photobiologic effects in the skin. The home suns emit short-wave UV radiation, particularly UVC radiation which produces initially erythema and after several days in indirect pigmentation or tan of the skin. On the other hand, high doses of longer UV-rays (UVA) lead to a direct pigmentation without the occurrence of erythema. The maximum of skin sensitivity to direct pigmentation is at the wavelength of about 360 nm. The latter tanning process, however, is difficult to achieve with conventional home suns, particularly due to the fact that heat radiation may cause skin injury when the human body is too close to the irradiation apparatus.
The heat rays also cause excessive heating of the housing of the apparatus. The housing and the reflector must therefore be made of a heat-resistant material, and especially electrical conduits must be laid at a sufficient distance from the infrared radiation source. As a result, the construction of such devices is bulky. Moreover, infrared radiators arranged in the reflector space reduce the effective reflecting surface and consequently the overall reflector must be made larger in order to achieve the desired tanning effect. Another disadvantage of home suns using IR radiators is the relatively long cooling period required between individual operational periods. Evidently, the above disadvantages are less troublesome in the case of large solaria, but are felt especially when a portable, compact irradiation apparatus is to be designed. The infrared radiators are necessary in prior-art irradiation devices particularly for starting ignition and stabilization of UV gas discharge lamps.
In prior-art irradiation apparatuses, the radiation source is usually mounted in the focal point of a parabolic reflector, so that the reflected rays are transmitted parallel to each other in the direction of the exposed subject. As known, the effect of the reflected radiation is optimum when the rays impinge upon the body of a patient at right angles. Due to the fact however that the human body is not flat, it is necessary to continuously change the direction of incoming rays and the position of the irradiation apparatus. Such continuous adjustments require a correspondingly complicated mechanical design of the apparatus, or an uncomfortable and time-consuming adjustment. Also, the manufacture of parabolic reflectors is relatively difficult and expensive, and the resulting reflectors are bulky and inconvenient for installation in the apparatus housing.